I was thinking water because it will greatly slow the objects speed prior to impact

No it won't. Laws of hydraulics. Again, you'd be MUCH better off landing it in an empty, arid region. Then you can just drive up to it and cart it off.

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then you can hopefully magnetically dredge up the debris without having to excavate all the dirt that will be kicked up on top of the object as it burrows into the Earth's crust.

We have plenty of experience with excavating for minerals...and a concentrated mineral deposit underneath a couple meters of earth is trivial. Magnetically excavating heavy iron embedded in a sea floor is a much more expensive proposal.

The amount of gold/platinum/etc. you'd need to make it profitable would instantly make the price of gold/platinum on Earth crater (pun intended) so it's no longer profitable. You can't just go and mine thousands of tons of platinum and expect it to be worth something when you introduce that much onto the market. Kind of like the Spanish and New World gold.

I think that has to be the point. Platinum is an incredibly valuable industrial metal since it's such a good catalyst. If this works, cheap platinum could revolutionize whole fields (like hydrogen fuel cells, for example).

Not to derail the thread, but are extraterrestrial metals chemically distinguishable from terrestrial ones? I imagine there may be different isotope ratios.

Aside from isotope ratios, there shouldn't be any difference... atoms are atoms. That said, you are much more likely to find 'pure' metal ores rather than oxides like are commonly found on earth because of the lack of O2, water, and other chemicals that cause reactions. This isn't an issue with metals like gold and platinum, but can be for other metals that require some rather nasty refining processes.

As to using the material, precious metals are used a lot in electronics and other areas. Additionally, metals like iron, nickel, and cobalt are rarely used in spacecraft except where absolutely necessary because they are too damned heavy, and thus very difficult to launch. If you've already got the metal up there, then its possible to build large structures using these metals. For example, if you can refine steel in space, then large pressurized habitats can be made with the steel, rather than launching aluminum or composite structures from Earth. These more dense metals also offer some advantages (once in orbit) like better radiation shielding.

Not to derail the thread, but are extraterrestrial metals chemically distinguishable from terrestrial ones? I imagine there may be different isotope ratios.

They're probably going to be mixed with all kinds of odd elements that you wouldn't find in terrestrial metals. Iridium for instance is largely absent from the Earth's crust, but fairly abundant in asteroids.

We have plenty of experience with excavating for minerals...and a concentrated mineral deposit underneath a couple meters of earth is trivial.

Something hitting the ground at a couple kilometers per second is probably going to penetrate more then a few meters into the ground. A lot more

Looking at google, meteor crater in Arizona was caused by 150 foot rock, and it left a hole a mile wide and excavated a 750 feet deep with negligible metal actually ending up in the hole. In fact:

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Most of the meteorite was melted by the force of the impact, and spread across the landscape in a very fine, nearly atomized mist of molten metal. Millions of tons of limestone and sandstone were blasted out of the crater, covering the ground for a mile in every direction with a blanket of shattered, pulverized and partially melted rock mixed with fragments of meteoritic iron.

So basically, just dropping the metal on the ground resulted in almost no salvageable metal because the impact energy was sufficient to vaporize and then disperse the material.

Something similar will happen upon impact with water, meaning that same metallic mist is now spread across a submarine floor.

That being said, if one were to try to deorbit an asteroid, one would probably first mount thrusters on it (or other velocity-adjusting device) and attempt a soft landing, at which point dropping it on land isn't going to cause massive destruction. You're still going to lose a lot of material on the way in, depending on composition.

longhornchris04 wrote:

Virogtheconq wrote:

Not to derail the thread, but are extraterrestrial metals chemically distinguishable from terrestrial ones? I imagine there may be different isotope ratios.

Aside from isotope ratios, there shouldn't be any difference... atoms are atoms. That said, you are much more likely to find 'pure' metal ores rather than oxides like are commonly found on earth because of the lack of O2, water, and other chemicals that cause reactions. This isn't an issue with metals like gold and platinum, but can be for other metals that require some rather nasty refining processes.

I guess I was thinking along the lines of how the non-industrial diamond industry can identify where diamonds originated (and thus can maintain a price differential between diamonds found in jewelry versus those used industrially), but that wouldn't really apply for a metals market, since everything's getting refined and mixed into alloys anyways, which would spread around any identifiable markers.

We have plenty of experience with excavating for minerals...and a concentrated mineral deposit underneath a couple meters of earth is trivial.

Something hitting the ground at a couple kilometers per second is probably going to penetrate more then a few meters into the ground. A lot more

Looking at google, meteor crater in Arizona was caused by 150 foot rock, and it left a hole a mile wide and excavated a 750 feet deep with negligible metal actually ending up in the hole. In fact:

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Most of the meteorite was melted by the force of the impact, and spread across the landscape in a very fine, nearly atomized mist of molten metal. Millions of tons of limestone and sandstone were blasted out of the crater, covering the ground for a mile in every direction with a blanket of shattered, pulverized and partially melted rock mixed with fragments of meteoritic iron.

So basically, just dropping the metal on the ground resulted in almost no salvageable metal because the impact energy was sufficient to vaporize and then disperse the material.

you cant compare entry velocity of a common asteroid with a thrust vectored one. much less kinetic energy.

you cant compare entry velocity of a common asteroid with a thrust vectored one. much less kinetic energy.

Further, even if you could stick thrusters on it, and it managed to maintain structural integrity all the way to a soft landing - it would require as much power and fuel to manage as it would to launch said asteroid from the surface of the Earth and bring it to space at the point and speed of its initial reentry (assuming of course you want to bring it down slowly enough to not ablate most of the thing during reentry).

Which will make it even less commercially viable.

The problem isn't that harvesting asteroids is technically impossible - I'm certain we could do it with essentially no better technology than we have today. The problem is the ROI sucks. It's the same reason why we don't bother extracting gold from seawater. Yes, it's technically possible, but why would you want to? It would cost orders of magnitude more money to do it than you'll ever manage to get out of it.

At some point in the future we may find ourselves in a situation where mining asteroids is the best solution to whatever problem we're facing, but at the moment I can't really imagine a situation where that would be the case while we're still confined to Earth.

Thinking about this a little more... so, its obvious that robots will be relied upon to mine and process the asteroids in orbit. This will take a whole lot of power, will they create nuclear robots? Solar powered? Or perhaps invent new processes to get at the minerals?

The asteroids that wikipedia is talking about are typically moving at tens of thousands of miles per hour relative to earth. An asteroid that we're driving would not have nearly that kind of speed.

And you really, really don't want to drop this thing in water....it would be MUCH safer to drop it into the middle of a desert in Africa or Australia.

In one animations I saw, the asteroid would be cut into a smaller piece, then encapsulated inside a flexible material that would then be steered into re-entry, I assume there were be a parachute involved. Once a process like this is perfected, production costs of these capsules would go down exponentially.

So basically, just dropping the metal on the ground resulted in almost no salvageable metal because the impact energy was sufficient to vaporize and then disperse the material.

This would happen with water as well, with a standard asteroid coming at us through natural means regardless of whether or not it hit water. Dropping a rock into water means you basically get a lot of slowing from the atmosphere, and then a full-on stop when it hits the water. Water is not soft. It is not forgiving. This is not high school diving class.

Furthermore, water has a huge, huge problem. It conducts energy away from the point of impact, in a near-perfectly lossless fashion. We have evidence of a few hundred thousand tons of rock falling at a modest angle, from the height of a less than a few thousand feet, creating waves over 100 feet high. And that was just rock and dirt, loosely packed.

A highly dense package of metal (asteroids are mostly iron) coming in at terminal velocity would create a MASSIVE splash. And by 'splash' I mean "huge wave that is likely to kill people and destroy property."

If you're going to drop it, drop that rock in a desert.

Like I said before, though...it makes way more sense to drop it on the moon...or as others have said, leave it in orbit.

500 tons of material, regardless of composition, at 1,000 km high has 4.9x10^12 joules of energy due to gravitational potential and, if in a circular orbit (17,700 km/h), has 2.1x10^16 joules of kinetic energy.

This is 5 megatons of energy.

Drop that sucker somewhere you don't mind losing, because you'll lose it and the impactor.

You must also put IN this amount of energy to land it anywhere close to recoverably.

And it's steered in for a controller reentry at a shalow angle at about 16,000 miles per hour initial velocity.

A space rock comes in at 50,000 mph and crashes straight in.

Like I said, surf's up in Kansas if it hits the ocean. You really REALLY don't want to hit water.

Using a carrot method (attractor) or attached thrusters over a course of many years to steer a rock into entering Earth orbit and then process it in orbit? That would be doable. Especially if you've got shipyards in orbit where you could use the material.

Sending it down to Earth in one piece isn't going to happen. Crashing it is a Really Bad Idea(tm) for two reasons: you may kill a million people, and you may lose the whole thing upon re-entry. Soft landing would cost more than what you could get out of the rock.

^ And, given the cost of heavy lift to orbit, it's more valuable up there anyway.

Yep.

As mentioned, if we're going to land it anywhere, the Moon would be the place to do it. At least there with 1/6 the gravity it'll be a LOT cheaper and easier and safer to do.

IF we can get orbital processing/refining and production/manufacturing facilities up and running, and IF we have an actual need to send something large enough beyond Earth orbit that doing so would be worthwhile, capturing asteroids as a source of raw materials might start to make economic sense.

I can see capturing a asteroid and moving to an orbit where you can get to it more easily, the next step of breaking it down and refining it into goods, then using those goods to build spacecraft seems like a much more complicated problem.

I can see capturing a asteroid and moving to an orbit where you can get to it more easily, the next step of breaking it down and refining it into goods, then using those goods to build spacecraft seems like a much more complicated problem.

Spacecraft construction is hard enough on Earth.

But you gotta take those 1st steps.

Actually, I'd say the hardest step isn't going to be construction, its going to be the extraction/refinement step. It takes a lot of technology and energy to turn ores into metals... even the basic stuff. Mankind has refined its techniques since the bronze age, but they all rely on having a couple of basic things, like 'cheap' energy and gravity that we take for granted.

One of the biggest problems for spacecraft is how to dump excess heat from the vehicle. As an example, if the space shuttle's cargo bay doors don't open, they have to abort and return to Earth within a few revs as the vehicle will overheat. Now, that's simply providing power for the shuttle's system and maintaining a room temperature habitat. How much waste heat will there be trying to to run a smelter? What about overcoming the fact that most refinement processes rely on gravitational separation, at least at the early stages? Where's the energy going to come from?

The basic technology required for this already exists, but not the implementation. This is one of the reasons why water is such an easy choice, the "use" side is already there. If you put 1000lbs of water in space today, it would have instant usefulness to the ISS or other habitable spacecraft... 1000lbs of iron not so much. But, once you show that its cheaper, or at least cost-effective, to "live off the land" then it opens up more possibilities.

I'm guessing solar powered lasers and centrifuges but I haven't seen any sort of hints or designs for space based extractive metallurgy systems, it may be you can get away with techniques (chemicals/explosives) that you can't do on Earth for environmental reasons.

Not to derail the thread, but are extraterrestrial metals chemically distinguishable from terrestrial ones? I imagine there may be different isotope ratios.

Aside from isotope ratios, there shouldn't be any difference... atoms are atoms. That said, you are much more likely to find 'pure' metal ores rather than oxides like are commonly found on earth because of the lack of O2, water, and other chemicals that cause reactions. This isn't an issue with metals like gold and platinum, but can be for other metals that require some rather nasty refining processes.

As to using the material, precious metals are used a lot in electronics and other areas. Additionally, metals like iron, nickel, and cobalt are rarely used in spacecraft except where absolutely necessary because they are too damned heavy, and thus very difficult to launch. If you've already got the metal up there, then its possible to build large structures using these metals. For example, if you can refine steel in space, then large pressurized habitats can be made with the steel, rather than launching aluminum or composite structures from Earth. These more dense metals also offer some advantages (once in orbit) like better radiation shielding.

So mine asteroids to set up space factories, and zero-g fabrication?

Yes? That makes a lot of sense how weight restrictions prevent any heavy-duty machinery from being blasted up there.

Well, one would build things a little bit at a time. Send up the required heavy machinery to be able to extract resources and stockpile them. Then send up the required heavy machinery to use those resources to build larger machines (sort of like a von Neumann machine). You don't have to lift the entire factory - just the pieces needed to be able to build it if a number of the raw materials can be found on-site.

Well, one would build things a little bit at a time. Send up the required heavy machinery to be able to extract resources and stockpile them. Then send up the required heavy machinery to use those resources to build larger machines (sort of like a von Neumann machine). You don't have to lift the entire factory - just the pieces needed to be able to build it if a number of the raw materials can be found on-site.

Bingo. Easier said than done but if we as a species are going to do anything beyond taking a few short trips to other bodies in this solar system we need resources that aren't stuck in a deep gravity well. That also means developing the technology necessary to extract said resources.

Now, a good 1st step would be to get some asteroid samples back to a Earth so we can get some reliable information about their makeup, consistency, etc so that techniques and technologies can be developed to extract resources from the asteroids. Right now its all ideas with nothing to back them up, actual experiments are needed to fully develop and prove out the technology.

Now, a good 1st step would be to get some asteroid samples back to a Earth so we can get some reliable information about their makeup, consistency, etc so that techniques and technologies can be developed to extract resources from the asteroids. Right now its all ideas with nothing to back them up, actual experiments are needed to fully develop and prove out the technology.

Well, we don't necessarily need a lot of sample returns - one advantage of parking it cislunar is the relative ease of access for probes. We can do a pretty good job with just some chemical assays and spectral analysis. Yes, eventually one would want to bring samples down (for the geologists if nothing else), but missions get a lot lighter if you don't have to worry about sample return.

Putting a nuclear power plant (or even fusion) would be a no brainer. Not like there would need to be any environmental impact assessments eh?

Only if you get it high enough, i.e. the orbital decay is longer than x half-lifes of the nastiest radioisotopes to provide sufficient radioactive decay. This will be based on the decay curve and how much crap... but MEO is far enough and easy enough to get to.

Putting a nuclear power plant (or even fusion) would be a no brainer. Not like there would need to be any environmental impact assessments eh?

Why not use solar? Less weight to get up, none of the nastiness if anything goes wrong.

Power density and longevity are the first things that come to mind. A 'final solution' booster motor that could send the beast into a decaying orbit into the sun might be possible as well, thus eliminating disposal issues.

Cooling a nuclear reactor is a significant issue, since it all has to be radiated away. Not sure if the radiators that would be needed to support the reactor would be competitive with solar.

The whole point is to be as efficient as possible...so having near-zero nodes on your system mean you can have a very efficient heat engine. Converting most of that heat to electricity removes the majority of the problem. The russians have used fission successfully, and we currently use RTGs quite well (and they last for decades in extremely harsh conditions).

As for radiators, I can imagine all manner of efficient designs including molecular-thin wire 'hair' covering purpose-built device, with the hairs standing out for hundreds or thousands of meters. The electricity itself could be beamed to more useful areas via microwave.

The main reason cooling nuclear systems on earth is such a big deal is gravity. It pulls molten slag down. This tends to hit groundwater, which becomes a nasty, nasty puff of steam.

In space? At worst you end up with a dully glowing lump of metals, that used to be in the shape of a power generator.

The whole point is to be as efficient as possible...so having near-zero nodes on your system mean you can have a very efficient heat engine. Converting most of that heat to electricity removes the majority of the problem. The russians have used fission successfully, and we currently use RTGs quite well (and they last for decades in extremely harsh conditions).

I'm not fully up on my nuclear lingo - what do you mean by near-zero nodes?

Alamout wrote:

...at worst, it's in a rapidly decaying orbit. At best, it's leaving an incredible hazard for anything else sent into orbit.

I don't think a reactor in a NEO is really that much of a hazard as long as it stays up. It's not like it's in LEO or even GEO waiting to crash into something - and even if it did collide, the radioactive material is going to be spread around enough to reduce the radiation risk to near zero.

Something the size of a terrestrial reactor re-entering the atmosphere could pose an issue, though, unless it were designed to jettison its fuel before it re-enters to ensure it gets spread around a sufficiently large area.

A typical naval reactor, which is the design that would be well suited for being put into space, is a 500 MW thermal. How would we pull 500 MW of heat off the reactor using nothing but radiated heat is beyond me.

Even the smallest reactor ever made (Toshiba S4) is 30 MWt. That's an astonishing amount of heat to deal with in the vacuum of space.

Not to derail the thread, but are extraterrestrial metals chemically distinguishable from terrestrial ones? I imagine there may be different isotope ratios.

As I understand it, most platinum-family metals mined on earth are ET in origin anyway, because the ones here when the earth formed all sank into the core and are still there.

Define "ET in origin".

Anything heavier than lithium had to originate in a star, and anything heavier than about iron required a supernova to form. So if you go back far enough, pretty much everything we've got here on Earth was "ET in origin", since it wasn't and couldn't have been created here, even by our own sun.